He doesn't adhere to the rigid canon that the fans believe should be gospel.
See, what creates the problem here is the way the books have been misleadingly promoted as "canon." Of course the makers of new onscreen
Star Wars aren't going to feel restricted by what the books do, since the books are going to be read by maybe 1-2% of the filmgoing audience. The movies and TV shows are the bigger moneymakers by far, so naturally they're going to be given total creative freedom to do whatever they want; the books and comics, much smaller pieces of the pie, have to follow the screen canon's lead, not the other way around. The screen canon is free to draw on ideas from the books and comics as it suits them, but is just as free to ignore or contradict them as it suits them. That's how tie-ins always work, unless the actual showrunner is writing/supervising them personally (as in the
Babylon 5 novels outlined by JMS, the
Buffy comics "executive produced" by Whedon, and the
Gargoyles comics written by Greg Weisman). So it was a false promise on the part of Lucasfilm to claim the books were ever canonical.